Experimental studies of ion-neutral reactions under astrophysical conditions

Abstract

Ion-neutral collisions are pivotal for the gas-phase synthesis of complex molecules in the interstellar medium. Accurate modeling of the astrochemical network relies on precise laboratory data of reaction rate coefficients and their branching ratios. For the majority of ion-neutral reactions, rate coefficients at astrophysical conditions are completely unknown. To gain an experimental insight of ion-neutral, gas-phase chemistry under interstellar conditions, two different experimental approaches are presented. One of the most fundamental ions for interstellar chemistry is H3+ . This ion is assumed to be thermalized in collisions with H2. However, recent astronomical observations of H2 and H3+ in diffuse interstellar clouds revealed a significant difference in their excitation temperatures. In this work, 22 pole trap measurements, performed at the Max Planck Institute for Nuclear Physics (MPIK) in Heidelberg, of the H3++ H2 reaction at thermal equilibrium are presented and discussed. For future experiments on ion-atom reactions, an injection beamline for the Cyrogenic Storage Ring (CSR) was developed to perform merged-beams experiments on neutral ground-state atoms superimposed with the cooled, stored ions in the CSR